Polyethylene (PE) resin is a thermoplastic plastic polymerized from ethylene homopolymerization and ethylene/α-olefin copolymerization, and is one of the general plastic products with the maximum production and consumption in the world. PE primarily includes low density polyethylene (LDPE), linear to density polyethylene (LLDPE) and high density polyethylene (HDPE), as well as some other polyethylenes having special properties. In terms of the consumption, the main use of LDPE is still will focus on film, piece products and plastic injection products; And in HDPE, consumption structure, blow molding and injection products will be the main application fields. PE has excellent mechanical behavior, electric insulativity, chemical resistance, low temperature resistance and processability, and PE articles are widely applied in various fields, such as industry, agriculture, packing and daily life.
Currently known PE catalysts mainly include Ziegler-Natta (Z-N) type catalysts, chromium catalysts, metallocene catalysts and some other non-metallocene catalysts. Chromium catalysts are very popular in the market due to its prominent contribution to HDPE production and the unsubstitutability of the product thereof. Even today about 50% HDPE is still produced therefrom.
J. P Hogan and R. L. Bank reported in U.S. Pat. No. 2,825,721 a silica gel-supported chromic oxide catalyst, i.e. best known Phillips catalyst. Leonard M. Baker and Wayne L. Carrick disclose in U.S. Pat. Nos. 3,324,101, 3,324,095 and CA759121 an organic chromium catalyst, i.e. S-2 catalyst produced by Union Carbide Company. Although the structure of these two catalysts is almost same, there are different catalytic and polymerization behaviors. Phillips chromic oxide catalyst has high polymerization activity, short induction period; S-2 organic chromium catalyst has low polymerization activity, long induction period, but the product has wider molecule weight distribution. Both of them can satisfy different market requirements and have been widely used.
Although there are various polyolefin catalysts, there are still the requirements on the catalysts having novel properties.